Utility scale energy storage is needed to balance rapidly varying outputs from renewable energy systems such as wind and solar. In order to address this need, an innovative utility scale energy storage concept has been created by the Precision Engineering Research Group (PERG) at MIT. The concept is to build hollow concrete structures to act as lower reservoir, install pump/turbine units, deploy them under the ocean and use the hydrostatic pressure of the water column as an upper reservoir to run the turbine and generate electricity, and pump the water out of the structure to store energy. The result is similar to a conventional Pumped Storage Hydroelectric (PSH) facility that operates on land using lakes and dams. Evolution of the ORES project will be presented and design iterations discussed in detail. Each design option is evaluated to better understand advantages and disadvantages. Concrete related tests were conducted to develop manufacturing process and evolve design assumptions. Global sites are evaluated for ORES deployment including an intensive study on the Mediterranean and Japan. Our research shows that storing energy underwater is technically and economically feasible and has great potential. Our geographical evaluations show that the Gulf of Maine, off coast of California, Hawaii, Mediterranean and Japan have great potential for both wind and ocean depths that favor ORES deployment.